Conventional plasma arc cutting torches produce a transferred plasma jet with current density that is typically in the range of 20,000 to 40,000 amperes/in2. High definition/high performance torches are characterized by narrower jets with higher current densities, typically about 60,000 amperes/in2. High definition/high performance torches are desirable since they produce a narrow cut kerf and a square cut angle. They also have a thinner heat affected zone and are more effective than conventional plasma arc cutting torches at producing a dross free cut and blowing away molten metal.
In plasma arc cutting, one effective way of producing the high quality cuts afforded by high definition/high performance torches is to utilize a vented nozzle design, such as is disclosed in U.S. Pat. No. 5,317,126. In a vented nozzle design, a portion of the plasma gas flows through the nozzle exit orifice used for cutting and the remaining portion of the plasma gas is bled or vented out of the nozzle prior to entering the nozzle orifice. Such vented nozzles produce straight and square cutting edges, small cutting kerfs, and achieve higher cut speeds without dross.
Prior vented nozzles are limited as to the torch conditions that they can withstand. For example, vented nozzles have not been successfully implemented for plasma cutting processes requiring greater than 200 amperes. Upon exposure to amperage conditions greater than 200 amperes, prior nozzles become too hot and, as a result, one or more of: an arc fails to form, double arcs form, cut quality suffers, nozzles melt, portions of the nozzle char, and portions of the nozzle become deformed.